1. Field of the Invention
This invention relates to a charged beam writing technique which writes a fine device pattern for a semiconductor integrated circuit or the like on an object by using a charged beam, in particular, a charged beam writing apparatus and writing method adopting a beam shaping system.
2. Description of the Related Art
In conventional art, there have been used a method of transferring a pattern by light, and a method of writing a pattern by using a charged beam such as an ion beam and an electron beam, to form the pattern on a substrate such as a semiconductor wafer and a mask. In particular, there has been mainly used an electron beam writing apparatus adopting a beam shaping system, in which an electron beam radiated from an electron beam source is shaped into desired shape and size and a pattern is written on a substrate by using the shaped beam, to manufacture a mask to be used for a lens projection aligner.
In an electron beam writing apparatus adopting a beam shaping system, writing of an internal portion of a pattern is performed by using a beam of a maximum size, i.e., a beam of an upper-limit size, which is provided by a beam shaping unit of the beam writing apparatus, and a contour portion of the pattern is divided by a figure having a beam size restricted in view of the space-charge effect and writing of the contour portion of the pattern is performed by using a beam of the restricted beam size (for example, refer to Jpn. Pat. Appln. KOKAI Pub. No. 59-167018, and Jpn. Pat. Appln. KOKAI Pub. No. 2-138723). In this method, a fixed beam size is used in the pattern contour portion, and thus no difference in the beam size is generated between individual figure portions in the pattern contour portion. Specifically, no difference in the beam resolution is generated between the individual figure portions in the pattern contour portion. Further, the internal portion of the pattern is divided by a large figure, the number of the figure portions is reduced, and increase in the writing time can be suppressed.
However, when the inventor of the present invention actually wrote a pattern by using an electron beam writing apparatus of the above method, actually there was decrease in the writing accuracy considered as being caused by the space-charge effect. It is inferred that this is because the beam size used in writing in the apparatus is different from the beam size in focusing. In an electron beam writing apparatus adopting the beam shaping system, focusing is performed by using a beam of a desired size prior to writing.
As described above, in the conventional electron beam writing apparatus adopting the beam shaping system, the beam resolution in writing is different from that in focusing due to the space-charge effect, and thus patterning accuracy is decreased with this.